1. Field of the Invention
The present invention relates to a toner used in a recording method that utilizes an electrophotographic process, an electrostatic recording process, an electrostatic printing process, and a toner-jet recording process.
2. Description of the Related Art
Heretofore, an electrophotographic process has been known as one that obtains a toner image by forming an electric latent image on a photosensitive member by various means utilizing a photoconductive material and subsequently developing the latent image with toner, followed by optionally transferring the toner image to a transfer member such as paper, and fixing the toner image on the paper by the action of heat, pressure, both of heat and pressure, or solvent vapor. In recent years, the image qualities of copies and printed images have been demanded much better than before as the digitalization of copying machines and printers has progressed. Based on such a demand, for improving the reproducibility of dot, there is a need of making toner into finer particles than before. Making toner into fine particles is effective for improving resolving paper or sharpness of an image, but may occur various kinds of problems.
For instance, the surface area of the toner increases when the particle size of toner is made small. As a result, the width of charge amount distribution increases, so that fogging that the toner is developed on a non-image portion would be easily caused. In addition, the charge characteristics of the toner become more susceptive to an influence of the surroundings. Also, an attempt has been made to make a sharp distribution of particle sizes for decreasing the fog or the like. However, such an attempt becomes a cause of increasing the manufacturing cost of toner. In additions such an attempt causes the performance of toner to be further affected according to whether the dispersibility of a binder resin and other internal additives is good or bad. With regard to such problems, as a method of providing the toner with desired frictional charge characteristics, the addition of a charge control agent into the toner has been known.
So far, the following charge control agents have been known in the art. That is, negative frictional charge control agents such as metallic complex salt of mono-azo dye, and metallic complex salt of hydroxy-dicarboxylic acid, dicarboxylic acid, and aromatic diol; and a positive frictional charge control agents such as nigrosine dye, azine dye, triphenylmethane-based dyes and pigments, quaternary ammonium salt, and polymers having quaternary ammonium salts on the side chains thereof. However, most of these charge control agents are being colored, so that most of them cannot be used in color toner. Furthermore, depending on the charge control agent, there are several problems with respect to the application to toner, such as difficulty in adjusting the image density and the degree of fogging in balance, difficulty in obtaining sufficient image density under high-temperature and high-humidity conditions, poor dispersibility to a resin, and adverse effects to storage stability, fixability, and offset resistance.
In recent years, in terms of the frictional charge control and the safety, a charge control resin has been also studied. For the toner for which such a charge control resin is used, for example, a method is disclosed in JP 63-184762 A, in which a polymer of styrene monomer and 2-acrylamide-2-methylpropanesulfonic acid is used as-a charge control agent. In addition, JP 3-161761 A and JP 5-142853 A disclose a method which a polymer of styrene monomer and 2-acrylamide-2-methylpropane sulfonic acid is used as a charge control agent to a polyester resin. According to these methods, the resulting toner is described as one having excellent optical characteristics and charge characteristics.
However, each of the methods described above has a problem in that the method cannot realize a stable developing performance irrespective of the usage situation, because such a problem is caused as the characteristics of a toner tend to vary depending on the factors of environmental variation, change with time, or the like when applied according to a desired image-forming process, as in the case of making the toner into finer particles or adopting a one-component developing system for attaining a high image quality.